The ability to vary the parameters such as the energy bandgap, carrier mobility, and thermal conductivity of semiconductor materials is crucial to the making of certain semiconductors devices. Actually this involves the making of new semiconductor materials. Devices such as infrared filters and detectors, visible and infrared emitting diodes and heterojunction devices with certain capabilities require semiconductor compositions with properties intermediate or outside the range of conventional semiconductor materials. A method used to achieve these non-conventional properties is by forming a solid solution of two or more semiconductor materials.
However, many alloyed semiconductor materials which are of considerable interest for making devices have components which are not readily miscible or are essentially immiscible in each other. Annealing for months or longer is required to achieve some measure of equilibrium with certain semiconductor materials and certain composition ranges of certain semiconductor materials. For example, InAS.sub.x Sb.sub.1.sub.-x alloys, which are sensitive to radiation between 3-12 .mu.m and are useful in infrared emitting diodes and detectors, take about three months to anneal, see Woolley, J. C. and Smith, B. A., Proc. Phys. Soc., 72, 214 (1958). Similarly Ga.sub.x In.sub.1.sub.-x Sb alloys require an annealing time of eight (8) weeks to achieve substantial equilibrium, see Woolley, J. C. and Smith, B. A., Proc. Phys. Soc., 72, 214 (1958).
Numerous techniques have been utilized experimentally to achieve miscibility more rapidly with certain compositions and ranges of compositions. In bulk materials, directional freezing has, for example, been partly successful in alloying some compositions of InAs.sub.x Sb.sub.1.sub.-x, see Woolley, J. C. and Warner, J., J. Electrochem. Soc. 111, 1142 (1964). Zone recrystallization of InAs.sub.x Sb.sub.1.sub.-x alloys has also achieved a measure of success, although homogeneous compositions in the range 0.5 &lt; x &lt; 0.8 have been difficult to obtain, see Woolley, J. C. and Warner, J., J. Electrochem. Soc. 111, 1142 (1964). Quenching and Czochralski methods have also been used to produce semiconductor alloys, see Hilsum, C., "Proc. of the International Conference on the Physics of semiconductors", p. 1127, Dunod, Paris (1964), and Sirota, N. N. and Bolvanovich, E. I., Dokl. Akad, Nauk B.S.S.R. 11, 593 (1967).
Thin film techniques have also been able to extend the miscibility of certain compositions. For example, vapor quenching of metals, see Mader, S. in The Use of Thin Films in Physical Investigations, ed. J. C. Anderson, 1966, Academic Press, p. 433, splat cooling of Ga in GaSb, see Duwez, P., Willens, R. H. and Kelment, W. Jr., J. Appl. Phys., 31, 1500 (1960), and flash evaporation of several III-V Group alloys including (Ga, In), (As, P) and GaSb.sub.x P.sub.1.sub.-x, see Richards, J. L., in The Use of Thin Films in Physical Investigations, ed. J. C. Anderson, 1966, Academic Press, p. 416, have been found to produce homogeneous alloy layers in limited composition ranges between components which are not readily miscible in bulk form. These layers, however, are usually amorphous or polycrystalline, rather than epitaxial.
Formation of epitaxial layers is especially important where the electrical characteristics of the desired device are related to semiconductor parameters, such as carrier mobility, which are defect sensitive. No difficulty has been encountered in preparing alloyed layers of the various semiconductor compositions by epitaxial techniques, e.g. chemical vapor deposition and liquid phase epitaxy, when miscibility of the components is readily achieved in bulk form. However, with other semiconductor components where miscibility is limited in bulk, chemical vapor deposition and liquid phase epitaxy produce epitaxial films of only limited miscibility, see Stringfellow, G. B. and Greene, P. E., J. Electrochem. Soc., 118, 805 (1971).
The present invention overcomes these limitations and shortcomings. It provides a way of readily making substantially homogeneous compositions of previously repoted immiscible, slowly miscible or partially miscible semiconductor component materials. Moreover, the invention provides a way of producing these compositions, some of which are known and some of which are novel, in epitaxial layers.